This invention relates to a core for use in the manufacture of castings having ducts therein.
In foundry practice, when cavities are to be formed in a casting, cores are inserted into the casting mould. These cores are usually made of core sand bonded with a binding agent and are removed after the casting has been cast and cooled.
More recently, the problem has increasingly arisen of forming long, slender ducts, such as through ducts or possibly also intersecting or cut-off ducts, in the castings in order to integrate into the casting hydraulics or pneumatic lines, such as control lines, oil return lines and pressure lines.
Such elongate ducts cannot be made either sufficiently long or sufficiently slender with sand cores, because long, slender sand cores are much too likely to break both in manufacture and also during further processing, such as blacking and placing in the mould. Moreover, such cores are not sufficiently able to withstand the forces which occur during casting. Even when it is possible to introduce them undamaged into the mould, a relatively large wastage rate still always occurs. It is indeed possible to support such long, slender sand cores in the mould by means of core marks. However these core marks lead to undesired apertures in the casting, which must subsequently be closed again and which in any case constitute a defect. Moreover, sand cores require special measures for removing the gases produced during casting (in particular on account of the binding agent), since otherwise there is a risk or porosity being produced in the casting. The drawing off of the gases produced during casting usually takes place through further passages formed in the casting and leading upwards, which naturally give rise to additional, undesired holes.
The production of slender ducts, in particular those which are not straight, by means of sand cores is nevertheless still possible for diameters in the region of about 6 mm, although the aforementioned disadvantages must be accepted. It is however, simply no longer economic to make smaller diameters, of for example 5 mm and less, by means of sand cores. A way out of this difficulty hitherto used has been to drill out the ducts in the casting subsequently. This is complicated and expensive. Moreover it necessitates many additional auxiliary and cut-off bores when the ducts are curved, which again must subsequently be closed.
There is therefore a requirement for a core, which enables the production of long, slender ducts in a casting, without its use being adversely affected by a high susceptibility to breakage or high gas production. The task underlying the present invention therefore is to create such a core.